Question

REFLECT AND APPLY Suggest a reason why the proofreading step in protein synthesis takes place at the level of amino acid activation rather than that of codon-anticodon recognition.

Short answer

Proofreading at amino acid activation ensures correct amino acid incorporation, preventing errors that would occur at codon-anticodon recognition.

Step-by-step solution

Understanding the context

Protein synthesis is the process by which cells build proteins based on the genetic instructions encoded in DNA. This involves transcribing DNA into mRNA and then translating mRNA into a protein sequence.

Amino Acid Activation

Amino acid activation occurs when an amino acid is attached to its corresponding tRNA by an enzyme called aminoacyl-tRNA synthetase. This step ensures that the correct amino acid is linked to the correct tRNA.

Role of Proofreading in Amino Acid Activation

The proofreading step happens during amino acid activation. Aminoacyl-tRNA synthetases have a proofreading function that checks if the correct amino acid is attached to the tRNA. If an incorrect amino acid is detected, it is removed and replaced with the correct one.

Codon-Anticodon Recognition

Codon-anticodon recognition occurs during translation, where the mRNA codon pairs with the tRNA anticodon to add the appropriate amino acid to the growing polypeptide chain.

Why Proofreading happens at Amino Acid Activation

Proofreading at the amino acid activation level ensures that only the correct amino acids are brought to the ribosome. If proofreading occurred at the codon-anticodon recognition stage, errors would lead to the incorporation of incorrect amino acids into the protein, which could be detrimental to protein function.

Key concepts

Amino Acid Activation

Amino acid activation is the first critical step in protein synthesis. This process involves the attachment of an amino acid to its corresponding tRNA molecule.
This attachment is mediated by an enzyme called aminoacyl-tRNA synthetase. The activated tRNA, now linked to an amino acid, is known as charged tRNA, or aminoacyl-tRNA.
This charging ensures that the tRNA is ready to participate in translating the genetic code into a protein sequence.

Aminoacyl-tRNA Synthetase

Aminoacyl-tRNA synthetase is crucial for the accuracy of protein synthesis. This enzyme has two key roles:

• First, it catalyzes the attachment of an amino acid to its corresponding tRNA.
• Second, it has a proofreading function to ensure correct attachment.

Each aminoacyl-tRNA synthetase is specific to one particular amino acid and its corresponding tRNAs. This specificity is essential for the correct interpretation of the genetic code.

Codon-Anticodon Recognition

Codon-anticodon recognition is a crucial step during the translation phase of protein synthesis.
During this process, the mRNA codon pairs with the tRNA anticodon.
Each codon in the mRNA pairs with a specific tRNA carrying an amino acid, ensuring the correct sequence of amino acids in the growing polypeptide chain.
This precise matching guarantees that the protein being synthesized will have the correct structure and function.

Protein Synthesis

Protein synthesis is the overarching process by which cells generate new proteins.
It involves two main stages: transcription and translation. In transcription, DNA is transcribed into mRNA.
In translation, the mRNA is read by ribosomes to build a protein, following the sequence dictated by the mRNA.
This process is highly regulated and involves multiple steps to ensure accuracy.
One of the critical accuracy checkpoints is the proofreading done by aminoacyl-tRNA synthetase during amino acid activation.